共查询到20条相似文献，搜索用时 15 毫秒
1.
T. Hashimoto T. Hurst A. Suzuki T. Mogi Y. Yamaya M. Tamura 《Journal of Volcanology and Geothermal Research》2008
Volcanic eruptions can produce large magnetic field changes by thermomagnetic effects, especially when magma cools from high temperatures and acquires a permanent magnetisation from the Earth's magnetic field. After the 2000 eruption of Mt Usu, Japan, significant magnetic field changes were observed not only in the vicinity of the magmatic intrusion but also in an area some distance away that was unlikely to be at a temperature near the Curie Point. 相似文献
2.
Summary The changes of the anisotropy of magnetic susceptibility of igneous rocks, induced by a magnetic field, are studied. It is proved that changes in the degree of anisotropy of susceptibility and of the orientation of the susceptibility ellispoid of specimens occur due to the configuration of the domain structure under the effect of the magnetic field. The influence of this effect on the total anisotropy of rocks depends on the degree of anisotropy due to the shape factor and on the stability of the domain structure. A model concept is presented, explaining the qualitatively different pattern of the changes of the anisotropy of susceptibility under the effect of the magnetic field in various directions of the specimens. 相似文献
3.
新沂地电场日变化特征及频谱分析 总被引：1，自引：1，他引：0
通过对新沂地电场平静时段资料与地磁场资料对比分析,结果显示:新沂地震台地电场变化和变化磁场密切相关,其中NS向的主体变化和地磁场H分量的变化准同步;EW向主体变化虽与地磁场H分量变化有相同之处,但其变化形态与其反向,且不尽相同.运用快速傅里叶变换进行频谱分析,发现:新沂地电场NS向和EW向与地磁场H分量的优势周期存在不... 相似文献
4.
The velocity field of large-scale magnetic structures during fast reorganizations of the global solar magnetic field structure
has been analyzed. Some characteristic features of the velocity field have been found during these periods. At that time,
a considerable part of the solar surface is occupied by regions with low horizontal velocities, which correspond to the regions
of positive and negative velocity field divergence during the solar activity growth and decline phases, respectively. Such
character of changes in the velocity field during these periods agrees with the previously proposed scenario of magnetic field
variations during global reorganizations of the magnetic field structure. The average horizontal velocities during a Carrington
rotation and their divergence have been calculated for Carrington rotations from 1646 to 2006. Relatively slow regular variations
in these parameters as well as their abrupt changes, observed during different solar cycle phases, have been revealed. An
increase in the average horizontal velocity during the solar activity growth phase is most probably caused by relative motions
of the regions with a new emerging magnetic flux. We assume that abrupt increases in the average horizontal velocity divergence
are related to fast reorganizations of the magnetic field structure. 相似文献
5.
V. Urpin 《地球物理与天体物理流体动力学》2013,107(3-4):269-284
Abstract We consider the turbulent dynamo action in a differentially rotating flow by making use of a kinematic approach when the effect of a generated magnetic field on turbulent motions is neglected. The mean electromotive force is calculated in a quasilinear approximation. Differential rotation can stretch turbulent magnetic field lines and break the symmetry of turbulence in such a way that turbulent motions become suitable for the generation of a large scale magnetic field. The presence of shear changes the type of an equation governing the mean magnetic field. Due to shear stresses the mean magnetic field can be generated by a turbulent dynamo action even in a uniform turbulence. The growth rate depends on the length scale of the mean field being faster for the field with a smaller length scale. 相似文献
6.
震前电磁场和大地自电位的异常是重要的地震前兆现象．在零磁空间对超低频段的磁场和自电位的变化进行了岩石破裂的实验研究，细致地揭示出电场、磁场出现异常变化的全过程，对深入认识超低频电磁信号的微观机理具有重要的意义．实验发现，岩石受力后应变、电位和磁场的缓慢变化在空间分布上是首先在近破裂源处出现，继而随裂纹的发展而改变位置；在时间序列上先出现自电位异常，然后是超低频磁场的变化；在异常形态上，超低频电磁信号呈现出早期、中期、晚期3个阶段的明显差异．研究表明，岩石微破裂引起裂隙尖端处的电荷分离. 静电荷在局部区域的积累和运移，导致了自电位的脉冲状变化；而在主破裂阶段，积累电荷的急速运动形成瞬间电流，激发了脉冲式的磁场异常．本文详细介绍了这一综合实验的技术步骤和观测结果，并对地震电磁前兆的微观机理进行了探讨． 相似文献
7.
T.G. Emeleus 《Journal of Volcanology and Geothermal Research》1977,2(4):343-359
Volcano-magnetic effects provide a possible way of monitoring temperature or stress changes within a volcano. A systematic study of several volcanoes in and close to the Rabaul caldera in east New Britain, Papua New Guinea, has been made to identify those in which thermal changes would be expected to cause changes in magnetic field. Two out of nine were chosen as suitable for a programme of magnetic monitoring which commenced in February 1974 and is continued at approximately six monthly intervals. The main criterion used for selection is that the volcano must have a magnetic structure causing a strong anomaly in magnetic field with its source located where its temperature would respond to changing conditions in the volcano. In the first three years of monitoring, no thermomagnetic effects have been observed, but the ongoing programme may be a useful tool in the prediction of volcanic eruption. Estimation of the magnitude of possible field changes depends on determining a satisfactory model of the source of the magnetic anomaly and how the remanent magnetization of the source depends on temperature. The former is a standard problem in geomagnetism and may be solved by computer modelling methods. Measurements of the temperature dependence of thermo-remanent magnetization (TRM) for rocks collected in the Rabaul caldera show the latter to be a much more difficult problem to solve in detail. This is because the temperature range in which TRM changes most rapidly with temperature varies greatly from specimen to specimen, and depends both on the magnetic minerals present and the cooling history of the rock. Rocks from within the anomaly sources were not accessible so doubt remains as to how similar their magnetic properties are to those of rocks collected from the surface. Within this limitation, it is shown that for at least one of the volcanoes studied, changes of total magnetic field of several hundred nanoteslas (1 nT = 1γ) are possible prior to a future eruption. 相似文献
8.
The anomalies of electric-magnetic field and self-potential before earthquakes are important precursory phenom-ena.A simulating experiment study on the variations in ultra-low frequency(ULF)magnetic field and self-poten-tial during rock cracking was carried out in a magnetic field-free space.The results revealing in detail the whole process of the occurrences of electric and magnetic anomalises are significant for understanding the microscopic mechanism of ULF electric and magnetic signals.The experiment indicated that at the initial stage the slow changes in strain.self-potential and magnetic field with small amounts appeared firstly near the source of initial cracking,and then extended as the crack developed on.In the time domain,the self-potential anomaly emerged first and ULF magnetic field changes arose then.The shape of the ULF electric and magnetic anomaly varied ob-viously in early-,mid-and late-term of the test.The authors attributed the pulse-like changes of self-potential to the generationj and movement of the accumulated electric charges during the cracking caused by charge separation on the crack tips within the sample.While the magnetic pulses of shorter-period at the last stage of the test,may be induced by instantaneous electric current of the accumulated charege during the cracking acceleration.The technical method and the observational results of this experiment are given in detail and the microscopic mechanism of elec-tric and magnetic precursors before earthquake are discussd in the present paper as well. 相似文献
9.
V. A. Dergachev S. S. Vasiliev O. M. Raspopov H. Jungner 《Geomagnetism and Aeronomy》2012,52(8):959-976
Recent studies have shown that, in addition to the role of solar variability, past climate changes may have been connected with variations in the Earth??s magnetic field elements at various timescales. An analysis of variations in geomagnetic field elements, such as field intensity, reversals, and excursions, allowed us to establish a link between climate changes at various timescales over the last millennia. Of particular interest are sharp changes in the geomagnetic field intensity and short reversals of the magnetic poles (excursions). The beginning and termination of the examined geomagnetic excursions can be attributed to periods of climate change. In this study, we analyzed the possible link between short-term geomagnetic variability (jerks) and climate change, as well as the accelerated drift of the north magnetic pole and surface temperature variations. The results do not rule out the possibility that geomagnetic field variations which modulate the cosmic ray flux could have played a major role in climate change in addition to previously induced by solar radiation. 相似文献
10.
L. L. Kichatinov 《地球物理与天体物理流体动力学》2013,107(3-4):145-160
Abstract Fluxes of angular momentum produced by turbulence in rotating fluids are derived with the effects of a magnetic field included. It is assumed that the rotation is slow but that the magnetic field is of arbitrary strength. A mean magnetic field is shown to produce qualitative changes of the sources of the differential rotation rather than the quenching of differential rotation usually expected. A new equatorward flux of angular momentum arises through the influence of the toroidal magnetic field. The possibility of interpreting the torsional oscillations of the Sun as a consequence of the magnetic perturbations of the turbulent angular momentum fluxes is discussed. 相似文献
11.
Summary Results of computing the anomalies of the variable magnetic field, generated by a harmonically variable field of the H1,0-type in the model of a spherical Earth with an expressive bulge in the well-conducting part of the mantle, are presented. It was found that not only the radial, but also the tangential component of the magnetic field is disturbed above the bulge. The largest amplitudes of these changes can be observed over the area of the largest slope of the conductivity boundary if the exciting magnetic field is perpendicular to the surface of the interface. 相似文献
12.
Many dynamic phenomena in the solar corona are driven by the complex and ever-changing magnetic field. It is helpful, in trying to model these phenomena, to understand the structure of the magnetic field, i.e. the magnetic topology. We study here the topological structure of the coronal magnetic field arising from four discrete photospheric flux patches, for which we find that seven distinct, topologically stable states are possible; the changes between these are caused by six types of bifurcation. Two bifurcation diagrams are produced, showing how the changes occur as the relative positions and strengths of the flux patches are varied. A method for extending the analysis to higher numbers of sources is discussed. 相似文献
13.
Ana G. Elias 《Journal of Atmospheric and Solar》2009,71(14-15):1602-1609
The Earth's magnetic field presents long-term variations with changes in strength and orientation. Particularly, changes in the dip angle (I) and, consequently, in the sin(I)cos(I) factor, affect the thermospheric neutral winds that move the conducting plasma of the ionosphere. In this way, a lowering or lifting of the F2-peak (hmF2) is induced together with changes in foF2, depending on season, time and location. A simple theoretical approximation, developed in a previous work, is extended to a worldwide latitude–longitude grid to assess hmF2 and foF2 trends due to Earth's magnetic field secular variations. Compared to the greenhouse gases effects over the ionosphere, the Earth's magnetic field may be able to produce stronger trends which vary with season, time and location. However, to elucidate the origin of F2-region trends, long-term variations in the three possible known mechanisms should be considered altogether—greenhouse gases, geomagnetic activity and Earth's magnetic field. 相似文献
14.
Magnetic reconnection at a three-dimensional null point is the natural extension of the familiar two-dimensional X-point reconnection. A model is set up here for reconnection at a spiral null point, by solving the kinematic, steady, resistive magnetohydrodynamic equations in its vicinity. A steady magnetic field is assumed, as well as the existence of a localised diffusion region surrounding the null point. Outside the diffusion region the plasma and magnetic field move ideally. Particular attention is focussed on the way that the magnetic flux changes its connections as a result of the reconnection. The resultant plasma flows are found to be rotational in nature, as is the change in connections of the magnetic field lines. 相似文献
15.
16.
针对岩层中介电常数和磁导率随深度变化的情况,给出水平磁偶极子源电磁场的水平或垂直空间分布特征及相应的变化规律。采用Kong给出的汉克尔（Hankel）J0变换线性滤波器（241点）和汉克尔J1变换线性滤波器（241点）算法,选用均匀大地和两层地电模型,讨论介质的介电常数和磁导率变化时的水平磁偶极子电磁场空间分布特征。计算结果表明,磁场的峨分量幅值与磁导率反相关;磁场H2和电场Ey分量随着磁导率的增大而增大;低频电磁测深中介电常数变化时对电磁场基本没有影响。 相似文献
17.
本文利用2019年和2020年两期的全国流动地磁矢量数据,针对玛多MS7.4地震震中附近的岩石圈磁场空间分布,分析研究了岩石圈磁场各个分量的震前变化特征。结果表明,玛多MS7.4地震发生前,震中附近的岩石圈磁场分量均发生了不同程度的变化:震中位于各分量的弱变化区域和零变线附近;震中位于各分量的高梯度带和低梯度带之间。本文证实了地震发生前会引起岩石圈磁场变化这一现象,并总结了震前地磁分量的变化特征,为今后强地震（尤其是M≥7.0地震）的震磁关系研究提供了一个震例参考。 相似文献
18.
Results of photospheric magnetic field extrapolation in a potential approximation and of the technique for separating the
open part of magnetic flux have revealed that changes in the relationship between the open part of the south polarity magnetic
flux obtained in the chromosphere and corona from July to November 2006 correlate with variations in the Akasofu parameter
calculated from data on the solar wind parameters and interplanetary magnetic field at Lagrange point L1, and with the K
p index. 相似文献
19.
Giuseppina Nigro 《地球物理与天体物理流体动力学》2013,107(1-2):101-113
This article addresses the interesting and important problem of large-scale magnetic field generation in turbulent flows, using a self-consistent dynamo model recently developed. The main idea of this model is to consider the induction equation for the large-scale magnetic field, integrated consistently with the turbulent dynamics at smaller scales described by a magnetohydrodynamic shell model. The questions of dynamo action threshold, magnetic field saturation, magnetic field reversals, nature of the dynamo transition and the changes of small-scale turbulence as a consequence of the dynamo onset are discussed. In particular, the stability curve obtained by the model integration is shown in a very wide range of values of the magnetic Prandtl number not yet accessible by direct numerical simulation but more realistic for natural dynamos. Moreover, from our analysis it is shown that the large-scale dynamo transition displays a hysteretic behaviour and therefore a subcritical nature. The model successfully reproduces magnetic polarity reversals, showing the capability to generate persistence times which are increasing for decreasing magnetic diffusivity. Moreover, when the system reaches a statistically stationary dynamo state, where the large-scale magnetic field can abruptly reverse its polarity (magnetic reversal state) or not, keeping the same polarity (steady state), it shows an unmistakable tendency towards the energy equipartition for the turbulence at small scale. 相似文献
20.
I. A. Bilenko 《Geomagnetism and Aeronomy》2012,52(8):1005-1014
This paper investigates the dependence of the observed coronal mass ejections and their parameters on evolutionary changes in the global solar magnetic field at different phases of solar cycles 23?C24. Four periods in the evolution of the solar cycle are identified, depending on the dominance ratio of the sectoral and zonal magnetic field structures. The parameters of coronal mass ejections observed during these periods are analyzed. The evolving structure in the global magnetic field is identified, and its influence on coronal mass ejections is examined. 相似文献